| The Cephidae is a family of the Symphyta,Hymenoptera with 170 species representing 25 genera in the world.Species of this family are phytophagous insects,thus the study on the phylogenetic relationships of Cephidae are of theoretical and practical values.Traditional morphological phylogenetics of Cephidae has been basically accomplished but the molecular phylogenetic study is limited by the molecular data yet.In this study,the second-generation sequencing method was used to sequence the mitochondrial genomes and 8 loci of single-copy nuclear genes of 8 species in 7 genera of Cephidae.The phylogenetic relationship was studied by combining the mitochondrial genome data of 13 species and the single-copy nuclear gene data of 10 species of Cephidae from NCBI.At the same time,the published mitochondrial genomes data of these 13 species and mitochondrial genomes of 2 species measured in the laboratory were selected as representative data to predict the secondary structure of rRNA,and the stem-loop was split and further analyzed.The main result are as follows:1.The length of mitochondrial genomes of the 8 species of Cephidae ranged from 15 468bp to 17 111bp,all containing 13 protein-coding genes,22 tRNA genes and 2 rRNA genes,the A+T content of the genome ranges from 75.2%to 83.3%,the overlap of genes is stable in some parts,but the variation of the gene gaps is large in Cephidae.The A+T content of the protein-coding genes are between 72.6%to 80.9%,except for the ATP8 start codons of Megajanus megamaculatus and Neosyrista incisa are TTG and the ND4 start codons of M.megamaculatus is GTG,protein-coding gene start codes of all other species are in standard ATN,and protein-coding gene stop codons are TAA or TAG.There is a significant correlation between the frequency of codon usage of protein-coding genes and nucleotide composition.All tRNA genes are the usual clover-leaf structure.Gene rearrangement occurs in all species,most types of rearrangement occur between rrnS and ND2.The rrnS gene length of the Cephidae ranged from 958bp to 1312bp and rrnL gene length from 1362bp to 1619bp.2.By the comparing research methods and referring to published data,the secondary structure of rRNA genes are predicted,and secondary structure pictures are drawn.The secondary structure of rrnS gene of Cephinae has two stems of H61 and H821,which are absent in other Symphyta species.The stem and loop of the secondary structure are split,and the conservation degree of each split stems is analyzed,the LOGO diagrams are drawn.The similarities and differences of the same of the 15 species are analyzed one by one.The results show that in the rrnS gene,the stems with higher detree of conservation are concentrated in the region Ⅲ,in the rrnL gene,the stems with higher degree of conservation are concentrated in the regions Ⅳand Ⅴ,while the stems with the lower degree of conservation are mostly with hairpin loopswhich having larger differences in the number of bases.3.In this study,multiple datasets including PCGs dataset,the stem-loop split datasets and single-copy nuclear gene dataets are used to study the phylogenetic relationship of Cephidae.The results shows that the Cephidae being classified into Cephinae and Hargigiinae based on traditional phylogenetics is supported by molecular data;but the sister group relation of Characopygus and Pachycephus is not supported by phylogenetic trees based on mitochondrial genomic data,therefore,the monophyly of Pachycephini is not supported.Characopygus is a member of Cephinae,and Pachycephus is a member of Hartigiinae and remote from Characopygus.Neosyrista incisa was placed into the genus Syrista,but the monophyly of Syrista is not supported by all phylogenetic trees,the genus Neosyrista need to be retrieved.As the monophyly of Janini in the subfamily Hartigiinae based on traditional phylogenetics is not supported,the tribal classification of Hargigiinae needs futher study. |
